Production of nitrophosphates



Patented Aug. 21, 1934 'umrso sra'rss' raranr OFFICE 1.911.111 rnonuo'non or m'rnomosrua'ms mu Hitcher and Samuel Basel,-

Bwitserland a No Drawing. Application May 20, mt, Serial No. c1s,ass..m Switaerland July 14. 1921 4 Claims. (0!. 71- -7) nitric acid and in U. 8. A. patent specification No.

1,293,293 (Foss) a 55-60% nitric acid has been recommended for the purpose. when employing nitric acid of such concentrations decomposition products are obtained which on cooling set to a solid mass containing a normal or even increased amount 0! water of crystallization, i. e. which contain their main constituents in the form of Ca(NOa):.4 H20 and Cal-hPzOul-hO. Even when employing nitric acid of somewhat higher concentration, for example a 62% acid, nitrophosphates are obtained which have a normal content of water of crystallization, particularly if the raw phosphates contain comparatively large amounts of calcium carbonate or ii calcium carbonate has been specifically addedthereto, since in the decomposition of calcium carbonate according to the formula CaCOa-l-2HNO:=Ca(NOa) a-i-HaO-I-CO:

more water is formed.

Nitric acid of higher concentration has hithertonot been employed for the production of nitrophosphates, presumably chiefly because it was feared that considerable losses of nitric acid would occur owing to the decomposition of the acid with the formation of oxides of nitrogen and least as much water as is required to enable its components to crystallize out with water of crystallization, i. e. that the main constituents, Ca(NO:)z.4HiO and CKHiPsOmHrO, can crystallize out, it being also stated that an excess of water amount to, for example, 1-2%, is not detrimental and may even frequently be neces- $811.

The nitrophosphates obtained according to the known processes and containing a normal amount a of water of crystallization are so deliquescent' that, even on standing for a short time in the air, they assume a pasty or viscous condition. The aioresaid nitrophosphates have, moreover, so low a softening point that they become sticky evenfrom the warmth of the hand, on which account and owing to their deficient keeping qualities and deficient capability of strewing, they cannot g5 be employed as fertilizers.

Thus, according to German patent specification No. 339,567, the nitrophosphate obtained by decomposition of raw phosphates with 60% nitric acid and containing readily deliquescent calcium I nitrate, is converted more or less extensively into the non-hygroscopic urea-calcium nitrate double salt. According to German patent specification No. 405,832, so much calcium sulphate is. added to the product obtained by decomposing raw phosphate with nitric acid that the calcium nitrate is converted into calcium sulphate. According to French patent specification No. 402,- 688, so much calcium carbonate or calcium oxide is added to the decomposition product that the water is fixed, whereby, however, the water-soluble phosphate obtained by the decomposition is again, to a large extent, re-converted into difficultly soluble diand tricalcium' phosphates.

According to the present invention a durable and storable nitrophosphate capable of being strewn is directly obtained by eflecting the decomposition of the raw phosphates with a nitric acid of. such concentration and in such quantity that the end product contains substantially less water than corresponds to the normal content of water of crystallization of the components contained therein.

Particularly valuable products suitable for fertilizing purposes are those which contain only as much water as corresponds mathematically to a calcium nitrate containing about 2-3 molecules of water. Acid-concentrations of about 65% to about 75% are,iin general, suitable for the production of such products. concentration and quantity of nitric acid employed are to be adapted to the quality and composition of the raw phosphate under treatment, the quantity and concentration of the nitric acid within the hereinbefore mentioned'limits being so selected that the water contained therein is not In other respects the nitrophosphate into tetrahydrate, but is only sufficient for the formation of the hereinbefore mentioned products containing only a little water of crystallization (only 23 mols of water per 1 mol of C8.(NO3)2). The quantity and concentration of nitric acid most suitable for the treatment of specific raw phosphate may be mathematically calculated or ascertained by a few prior tests.

The nitric acid may be employed in the quantity theoretically required for the decomposition or in slight excess thereof, always with the precaution, however, that no more water is thereby introduced into the reaction than is necessary for the formation of the desired nitrophosphates containing only a little water. Very high acid concentrations, for example those of and more,

are not suitable for the present process, since,-

apart from other disadvantages, the complete decomposition of the phosphate is rendered difiicult thereby both in a chemical and mechanical sense and a considerable part of the nitric acid is decomposed with the formation of nitrogen oxide and water.

By keeping to the aforementioned conditions of operation, there are obtained, after setting of the decomposition masses, products as hard as stone which can be readily ground and, after grinding,-

represent a satisfactorily storable and transportable fertilizer consisting of solid grains, and capable of being strewn, the softening point of which is considerably higher than the softening point of the known m'trophosphates of normal or increased water content.

e The effects obtainable by the invention could .air, to such an extent that the water content corresponds to that of the end products obtained according to the present invention, these products which have been subsequently converted into a form containing less water, are much more hygroscopic than the nitrophosphates obtained direct in a form containing only a little water by limiting the water content in the process of decomposition according to the invention.

It has further been found to be advantageous so to carry out the decomposition of the raw phosphates that the operation is first efiected at lower temperature and the reaction only completed towards the end of the decomposition process by heating more strongly. In this way it is possible to carry out the decomposition in such a way that losses of acid by decomposition with the evolution of oxides of nitrogen are, to a large extent, avoided.

It is known that nitrophosphates on storing evolve small quantities of oxides of nitrogen.

-Thls disadvantage is overcome according to the invention by admixing, with the nitrophosphate poor in water prepared according to the invention after the conversion of the same into a size of gram suitable for fertilizing purposes, such small quantities of urea that the individual nitrophosphate grains are covered with a thin layer of powdery urea. Admixtures of less than 2% are, in general, suitable for the purpose.

According to German patent specification No. 339,567 raw phosphates are decomposed with nitric acid and urea is added to the decomposition product before setting in order to convert 1,971,111 sufficient to convert the calcium nitrate of the the readlly deliquescent calcium nitrate into the double salt According to the present invention on the other hand, the finished nitrophosphate grains are only powdered on the surface with quite small quantities of urea in order to avoid the evolution of oxides of nitrogen.

A charactermtic of the German Patent No. 339,567 is that a 60% nitric acid is recommended for the decomposition process. The necessity of converting the nitrophosphates so obtained by chemical reaction with urea into a storable product capable of being strewn, proves that the nitrophosphate directly obtained was not per se serviceable owing to its high water content.

The avoidance of the development of oxides of nitrogen during storage by simply applying very small quantities of urea is of technical and economical importance in that not only is the disturbing smell thereby avoided, but also the destruction of the packing materials, (sacks).

Example The mass was thereafter worked up for some time longer, whilst the temperature was increased to 60-70 C. The homogeneous decomposition product yielded after 8 days storage, a stone hard mass. By comminuting the same a nitrophosphate poor in water was obtained in the form of hard grains which were not softened by the heat of the hand. After a storage period of several months, the product still contained 94% of water-soluble phosphoric acid.

The superiority of the process of the invention is shown in the following comparative experiments which were all carried out with the same morocco phosphate (containing 8.6% of calcium carbonate) of the following composition:-

Percent SiOz 1. 31 02.0 51.27 MgO 1.03 F6203 1. 52 25 A1203 0. 13 S03 1. 47 C02 3.78

F 2. '13 H2O at 110 C 1.73 P205 -L 33.33

Experiment 1 (according to the present invent on' After analyzing the raw phosphate under treatment, the concentration and quantity of nitric acid to be employed was so calculated on a stochiometrical basis that 1 mol. of water was present in the end product for every mol. of CaH4(PO4)z and 2 mols. of water for every mol. of Ca(NO3)z. As a result of this calculation of 1015 gms. of a 72.4% nitric acid were employed per 1000 gms. of raw phosphate. In order to compensate for losses, a further 2% of nitric acid was employed, i. e. a total of 1035 1 gm. The material converted after decomposition and setting into granular form showed the following properties? Softening point:42-44 C. Capability of resisting damp air:;-After tak- -ingup4%oiwaterthegrein|arestill Behaviouron' strewing:-'-The grains mm -tendencytoadheretothehandandremainccml pietely hard.

Experiment ziaecordino to known processes) For 1000 gms. or raw phosphate. 123cm. 60% nitric acid were employed. The decomposition in this case was rendered very diillcult owing to strong team formation. The decomposition product on setting termed a dry. somewhat porous solid mass.

Properties of the granular motorist-- Soitening point:-34-36 C.

' Capability oi resisting damp aim-Alter taking up 1% of water the grains are soit.

Behaviour on scattering:-'Ihe grains soften in a few minutes on the surface of the hand and betwen the fingers. They thereby smear and remain sticking to the hand.

Experiment 4 (according to known processes) For 1000 gms. of raw phosphate 1187 me. as 62% nitric acid were employed. After the decomposition product had cooled there remained a solid porous mass.

Properties of the granular materiai:-- Softening point:---8'i C.

Capability of resisting damp air:-,-Atter taking up 0.5-0.8% oi moisture the granular surfaces were smeary and sticiw. After taking-up 1.54% 01' moisture the grains were completely soft.

only 2 mole. of water per lmoL'o! CMNOs): it.

. '3 Behavioin'on sirewingr-e-Thegrainsstickio thesuriaceotthehandand'partiaiiymelt. *Ispcrimes t6(sceordingtoknowaproces:cel*

em- 1000 gms. or m phosphate 1210 me so nitric acid were employed so that thco' Y retically only about 04% oi'thephosphoric me could be converted into water-soluble form. 0!: setting oi the decomposition product only a semi-solid mass was termed which, undersiight pressure, flowed apart; aproduct cai'niblc oi strewing could not be obtained. from this Whatweclaimis:--- P g, 1. As a novel. fertilizer" a storable, transport; able nitrophosphatecapabie of being strewn, the water 0! crystallization content of which is so low that for 1 moi. of calcium monophosphate, 1 moi. of B10 is present and for 1 mol. oi calcium nitrate not more than 3 mols. are present. 2. As a novel fertilizer, a storabie, transport able nitrophosphate capable of being strewn, the water of crystallization content, of which is so low that per moi. of calcium monophosphate 1' moi. of B 0 is present and per moi. of calcium nitrate not more than 3 mole. of H10 are present 1 and the grains of which are covered with a thin layer of urea.

3. Process for the direct production oi storable and transportable .nitrophosphutes capable 'of being strewn, therein characterized. that raw 1 5 phosphates are decomposed with nitric acidot a concentration between and with the precaution that the quantity oi nitric acid employed is so selected that the decomposition product after. setting contains not more than 3 mols. of water per moi. of calcium nitrate.

4. Process for the direct production of storable and transportable nitrophosphates capable of being strewn therein characterized that raw phosphates are decomposed with nitric acid, the n; 

